The present invention is directed to an electroplating apparatus for plate-shaped workpieces which are conveyed through the apparatus in a horizontal plane and are particularly designed for handling perforated printed circuit boards. The apparatus has at least one anode arranged above the path and at least one anode arranged below the path extending parallel to the path and to the upper anode, electrolyte collectors or headers being directed transversely relative to the path and being arranged above and below the path at the inlet side and at the discharge side, respectively, said collector means having openings for the emission and removal of electrolytic solutions that are directed between the path and the upper or, respectively, lower anode.
An electroplating apparatus having an arrangement forming the path for transporting plates, such as printed circuit boards, in a horizontal direction through the apparatus between an upper anode and a lower anode, said apparatus having electrolytic header means extending transverse relative to the path at the inlet side and at the discharge side above and below the path with electrolyte collectors having openings for the emission and/or collection of electrolyte is disclosed in an allowed U.S. patent application Ser. No. 147,294, filed Jan. 22, 1988, which issued as U.S. Pat. No. 4,832,811 on May 23, 1989, whose disclosure is incorporated by reference thereto and which claims priority from German Application P No. 37 02 229, which was also the basis of published European Patent Application No. 0 276 725.
With an electroplating apparatus constructed in the above manner, the quality of the electro-deposited layers can be improved, particularly in view of the uniform distribution of the layer thickness, a high adhesion and a good ductility when compared to traditionally constructed electroplating devices.
The structure disclosed in the above-mentioned U.S. patent application is based on the perception that qualitatively high-grade surfaces of the electro-deposited layer can be guaranteed only on the basis of flow components of the electrolyte liquid directed in the throughput direction of the workpieces and that such flow components in the longitudinal direction can be realized by the described provision of the electrolyte headers. However, flow components, that are vertically directed onto the surface of the workpiece, should not be eliminated, since they can continue to be important for the production of through-contacts in the perforated printed circuit boards.
The flow components in the longitudinal direction can be produced both by the emission as well as by the removal of the electrolyte solution through the openings of the electrolyte headers. Especially beneficial results, however, are achieved when at least one of the electrolyte headers is intended for the emission of the electrolyte solution.
According to the preferred embodiment of the U.S. application, two electrolyte headers are intended for the emission or input and two electrolyte headers are intended for the collection of the electrolyte solution. Other improvements in the quality of the electro-deposited layer can be achieved, in this case, when the two electrolyte headers arranged at the outlet side are intended for the emission of the electrolyte solution. In other words, this means that the flow components in the longitudinal direction are directed opposite the throughput direction of the workpiece in the apparatus.
It has also proven especially beneficial, particularly in view of good flooding of the holes in the printed circuit board, when the electrolyte solution for the electrolyte headers intended for the emission can be supplied via separate pumps. An especially effective flooding of the holes can be achieved in that a greater quantity of the electrolyte solution is supplied to the electrolyte headers arranged above the throughput path than that which is supplied to the electrolyte header arranged under the throughput path. This is particularly advantageous when the workpieces are to be additionally washed from below.
According to a further development of the device in the above-mentioned U.S. application, it is provided that the openings are directed obliquely onto the throughput path at a slight angle of attack. As a result of this measure, which can be easily realized in structural terms, the exit or entrance orifice of the openings can be brought extremely close to the surface of the passing workpieces.
It has also proven advantageous when the openings are introduced into the electrolyte headers in the form of bores uniformly arranged over the width of the path. Given a low structural outlie when compared to through slots in the transverse direction, such openings enable a more uniform distribution of the desired flow components.
Finally, it has proven particularly beneficial when the upper anode is fashioned as a soluble anode having a soluble anode material arranged on a sieve-shaped or lattice-shaped carrier. The advantage of a soluble anode are, thus, achieved so that a constant distance from the passing workpiece is simultaneously guaranteed. In particular, the combination of such an upper anode with an insoluble, lower anode achieves optimum conditions in view of the scatter of the layer thicknesses and the distribution of the layer thicknesses on the surface of the workpiece, given simple maintenance of the electroplating apparatus.
However, when employing brighteners, a combination of the upper soluble anode and the lower insoluble anode can lead to an increased consumption of brightener. For this reason, a construction of the upper and lower anodes as soluble anodes is to be preferred when the electrolyte solution contains brighteners.